The invention relates to signal transmission systems, and is well suited for transmitting raster information signals from a television camera to a receiving station located a significant distance from the transmitter.
A TV camera outputs a signal that is a voltage vs. time waveform of the voltage levels, i.e., amplitudes of its scanned raster of periodic horizontal lines and includes synchronizing voltage pulses for the end of each horizontal line, for the end of each frame, and for in-phase or in-step generation of color by the TV set receiver. The camera's oscillator for color generates a color burst or brief cycles of 8 or 9 voltage pulses that are output by the camera as a component of the camera's output waveform that synchronizes the receiver oscillator with the camera's oscillator and are not frequency in themselves.
The output of the TV camera (NTSC) is a continuous voltage vs. time waveform of 525 horizontal lines by 30 frames per second. It is the sequential output of 15,750 horizontal line periods of 63.4 .mu.sec. each that make up the total TV picture each second. The waveform is the voltage information that permits the receiver to restore the camera's original scanned pictures, in color, by use of the receiver's own hardware that is synchronized with the camera by the transmitted TV camera's waveform of voltage information.
The color subcarrier is not output by the TV camera, nor is the TV camera output a modulated waveform. The camera's subcarrier generates a color burst of voltage pulses that are included in its waveform so as to be the color reference for the receiver's production of color from its own oscillator.
Generally, the complete waveform output from the TV camera is a voltage vs. time waveform of the voltage levels of the brightness of the scanned horizontal lines of the raster and the added horizontal, vertical and color sync voltage pulses that are the information required by the TV receiver to regenerate the TV camera's pictures which are formed from the images on a TV sensor, e.g., tube or pixels. When output from the camera, the waveform is not an amplitude modulated (AM) signal, nor is it a sampled signal.
It is significant that the color sync pulses (or color bursts) are voltage signals that are phase references for the 3.58 MHz oscillator in the color processing circuitry of the receiver. The color bursts are not output from the TV camera as a signal that has a 3.58 MHz frequency.
The horizontal lines of the TV camera's raster are periodic, and each line has a period of 63.4 .mu.sec (NTSC). The lines are the continuous periodic dc carrier of the voltage level information of the output voltage vs. time waveform that is the information for regeneration at the receiver.
The output of a color TV camera, therefore, is a composite color video signal that is the voltage information of the video generated by the camera to which are added sync pulses and color burst phase reference pulses. The 3.58 MHz color burst signal is suppressed. It is not actually transmitted, and the TV camera output is not a 3.5 MHz signal. It is known that the subcarrier provides the color information which the receiver must use to adjust its own 3.5 MHz subcarrier. The subcarrier activates a burst gate or burst generator that outputs a short sample of the subcarrier (e.g., 8 or 9 cycles) in the form of voltage that is added to the blanking signal. At the receiver, the burst voltage functions as a reference to keep the receiver's own 3.58 MHz subcarrier at the exact same frequency and phase as that of the 3.58 MHz suppressed subcarrier. The TV camera output is a composite color video signal comprising voltage information of the continuous sequential periods of the 525 horizontal lines of the raster (NTSC), from top to bottom, that have a period of 63.5 .mu.sec (color video).